linux-kernel - Re: [PATCH net-next v5 11/19] xdp: add generic xdp_buff_add

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Message-ID: <ZzYEFb4xK6IquBhI@shredder>
Date: Thu, 14 Nov 2024 16:07:17 +0200
From: Ido Schimmel <idosch@...sch.org>
To: Alexander Lobakin <aleksander.lobakin@...el.com>
Cc: "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Toke Høiland-Jørgensen <toke@...hat.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	John Fastabend <john.fastabend@...il.com>,
	Andrii Nakryiko <andrii@...nel.org>,
	Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
	Stanislav Fomichev <sdf@...ichev.me>,
	Magnus Karlsson <magnus.karlsson@...el.com>,
	nex.sw.ncis.osdt.itp.upstreaming@...el.com, bpf@...r.kernel.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v5 11/19] xdp: add generic xdp_buff_add_frag()

On Wed, Nov 13, 2024 at 04:24:34PM +0100, Alexander Lobakin wrote:
> The code piece which would attach a frag to &xdp_buff is almost
> identical across the drivers supporting XDP multi-buffer on Rx.

Yes, I was reviewing such a change when I noticed your patch. We will
use this helper instead. Thanks!

> Make it a generic elegant "oneliner".
> Also, I see lots of drivers calculating frags_truesize as
> `xdp->frame_sz * nr_frags`. I can't say this is fully correct, since
> frags might be backed by chunks of different sizes, especially with
> stuff like the header split. Even page_pool_alloc() can give you two
> different truesizes on two subsequent requests to allocate the same
> buffer size. Add a field to &skb_shared_info (unionized as there's no
> free slot currently on x86_64) to track the "true" truesize. It can
> be used later when updating an skb.
> 
> Reviewed-by: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
> Signed-off-by: Alexander Lobakin <aleksander.lobakin@...el.com>

Reviewed-by: Ido Schimmel <idosch@...dia.com>